Beale AFB is the SR-71 and U-2 home base. The SR-71 on display
is located under the tower near the flightline, an area that is
restricted and off-limits to civilians.

Update—as of 2008, the Blackbird has been moved from its old
location on the flightline to a new location near the main base
area of Beale AFB. This will hopefully allow more people to see
the SR-71, though it appears that access to Beale is still tightly
controlled since 9/11.